The present invention pertains to devices and processes for aerobic composting of organic matter. Organic waste matter such as animal manure, vegetative matter, food wastes and the like may be decomposed by action of aerobic, oxygen consuming, bacteria and similar organisms. This decomposition is often termed composting. Many processes and devices are available for carrying out and speeding composting of organic wastes. It is a common objective with these processes and devices to ensure sufficient available oxygen for efficient aerobic action. When decomposition occurs without oxygenxe2x80x94anaerobicallyxe2x80x94the decomposition by-products include noxious gases and undesirable materials.
Both to ensure thorough oxygenation and complete inoculation of the waste with bacteria, the composting material is often mixed, turned or tumbled in some manner. Air entrainment or injection is also attempted in some known processes. Mixing and addition of air is problematic in practical applications where large waste streams must be handled.
The U.S. Patent to Byrd (U.S. Pat. No. 5,766,225) is exemplary of many devices for small waste streams. A container is provided with a multiple of small container holes or openings through which air enters the container. The container may be rotated to mix the contained waste material. However, the Byrd devices are not practical for larger volumes. U.S. Pat. No. 5,759,850 to Seymour and U.S. Pat. No. 5,047,349 to Eweson disclose various other rotary containers for mixing and aerating waste materials for beneficial composting. One common weakness in these designs is the undue complexity and subsequent high cost of the devices. Their complexity often results in operational failure. A limitation of many of these devices and processes is due to the need to maintain relatively high operational temperatures. The inherent corrosive environment of the materials is an added difficulty. Peak efficiency of aerobic bacterial decomposition is achieved at temperatures in the range of 120 to 150 degrees. Although aerobic composting is exothermic, in cold climates such as in northern geographical regions, low ambient temperatures in winter require external heating of composting systems to maintain the desired temperature. Typically, this means the composting process must be operated within a temperature controlled space, adding to cost and complexity. What is needed is a composting device and system which is simple and that reduces the beat losses from the exothermic composting process.
The present invention is a device and method for efficient composting of organic matter using a low-cost composting structure and high efficiency methods. An inexpensive design incorporates low cost rigid insulated panels to form an insulated composting container of a generally cylindrical shape with polygonal cross-section. The insulated panels provide high thermal efficiency to help maintain composting temperatures. A rigid frame supports the panels and allows the container to be rotated. An internal manifold or plenum is located along the length of the container to supply air to a volume of waste matter contained in the container in use. An air supply is connected to the manifold to deliver air while the container is stationary or rotating. Rotation in various embodiments is effected by motor driven rollers bearing on external hoops integrated to the container support frame.
In a preferred embodiment, the container consists of eight panels forming an octagonal cross-section. The octagonal shape promotes mixing at a high fill level that is an improvement over cylindrical containers. This improved mixing of the present inventive device and methods makes unnecessary the internal mixing elements such as the screws and baffles used in many of the prior art devices. However, the use of such internal mixing elements is possible in combination with the benefits of the present inventive concepts.
The invention includes methods of composting in which the inventive device is rotated at relatively slow rates that induce intermittent tumbling of the composting matter. This action increases the mixing and aeration action to improve the biological processes and decomposition of the matter. In preferred methods, the container is at least partially filled with waste matter and rotated at rates slower than one revolution per minute as air is introduced. The container is alternatively rotated and held stationary for periods of time.
The invention may be more fully understood by reference to the following figures and details of exemplary embodiments. Alternative embodiments of the invention as claimed, and providing the benefits of the novel concepts of the invention, are contemplated and will be obvious from these explanations.